1. Field of the Invention
This invention relates to an impact sensing apparatus used as a sensor for starting the operation of a safety system such as an airbag or seat-belt tensioner to protect against impact.
2. Description of the Prior Art
A known example of a conventional shock sensing apparatus of this kind is disclosed in the specification of Japanese Patent Application Laid-Open (KOKAI) No. 60-248456. The apparatus includes a sensing cone the movement of which causes a rod to be urged and turned against the biasing force of a spring. Owing to the turning motion of the rod, a rotary shaft is rotated to disengage the rotary shaft from a firing pin, thereby allowing an output member to be moved by the biasing force of the spring.
With an impact sensing apparatus of this type, the damper effect of a fluid in a clearance between the sensing cone and a housing is utilized to prevent erroneous operation in such a manner that shocks sustained for extremely small periods of time, as when a vehicle is traveling on a bumpy road, will not actuate the impact sensing apparatus. A problem encountered in this arrangement is that the characteristics thereof change due to such conditions as a change in temperature, as a result of which stable operating performance cannot always be obtained.